Its an expensive & long process, you need to have your Betta housed in their own individual tanks to start off with, then you need a seperate breeding tank which needs to be bare bottomed.
The male & female have to be conditioned for a week to 2 weeks before hand, then they are slowly introduced to each other, when the male is placed in the breeding & the female is introduced using a chimney, the act of spawning can be quite aggresive & they need to be closely watched, once spawning has occured you need to remove the female immediately.
The male then cares for the eggs & young fry until they are free swimming, he is then removed & it is your job to care for the fry, they need tiny live foods, such as baby brine shrimp, banana worm etc which you have to cultivate yourself.
Once the babies start to mature, the males need seperating so you will need to be able to seperate them all into individual large jars, which will all need to be heated & have water changes done.
Its not easy, often extremely frustrating, expensive but very rewarding.
I'm really new to it all myself, if you look through all the info on here & other site you will find tons of information, with Betta breeding you need to read every little bit you can find.